Fuel reforming system

ABSTRACT

A fuel reforming system comprises a reforming catalyst section ( 4 ) performing reformate reactions on supplied fuel gas, a membrane hydrogen separator ( 5 ) extracting hydrogen from the reformate gas, a supply device ( 8–14 ) supplying combustion gas for heating the membrane reactor ( 2 ), a sensor ( 16 ) for detecting the temperature of the membrane hydrogen separator ( 5 ) and a controller. The supply device supplies combustion gas to the membrane reactor ( 2 ) before the reforming catalyst section starts reformate reactions during startup of the membrane reactor ( 2 ). Furthermore the supply device stops supply of combustion gas to the membrane reactor ( 2 ) when the temperature of the membrane hydrogen separator ( 5 ) is greater than or equal to a target temperature. Thereafter the fuel supply device supplies fuel to the fuel reforming catalyst section ( 4 ). In this manner, hydrogen embrittlement in the membrane hydrogen separator can be avoided.

This application is a 371 of PCT/02/08405 filed Aug. 8, 2002.

FIELD OF THE INVENTION

This invention relates to a fuel-reforming system.

BACKGROUND OF THE INVENTION

A type of fuel reforming system known from the prior-art comprises witha membrane-type hydrogen generator which separates hydrogen from areformate gas using a hydrogen permeable membrane (membrane hydrogenseparator). Tokkai 2001-135336 published by the Japanese Patent Officein 2001 discloses a fuel reforming system using this type ofmembrane-type hydrogen generator.

The strength of the hydrogen permeable membrane, and in particular, thestrength of a metallic hydrogen permeable membrane is reduced duringpermeation of hydrogen. This phenomenon is known as hydrogenembrittlement. Consequently the fuel reforming system must supplyhydrogen to the hydrogen permeable membrane taking such hydrogenembrittlement into account. Hydrogen embrittlement tends to occur at lowtemperatures in a metal membrane hydrogen separator such as a palladiummembrane or a palladium alloy membrane.

SUMMARY OF THE INVENTION

However the above type of prior-art fuel reforming system does notconstitute a sufficient solution to the problem of hydrogenembrittlement. In particular, when starting the fuel reforming system,hydrogen produced by the reformer is supplied to the membrane hydrogenseparator when the temperature of the membrane hydrogen separator is ata low level. Thus when hydrogen is supplied to the membrane hydrogenseparator at a low temperature, hydrogen embrittlement results in themembrane hydrogen separator and this reduces the permeability of themembrane hydrogen separator.

It is therefore an object of this invention to provide a fuel reformingsystem which can avoid hydrogen embrittlement at low temperatures.

In order to achieve above object, this invention provides a fuelreforming system comprising a membrane reactor having a reformingcatalyst section for reforming a supplied fuel gas to a reformate gas, amembrane hydrogen separator for separating hydrogen from the reformategas, a hydrogen passage for transferring hydrogen separated by themembrane hydrogen separator to a fuel cell, and a combustion catalystsection for heating the reforming catalyst section; a first supplydevice for supplying combustion gas to the membrane reactor, the firstsupply device having a combustor for producing the combustion gas; asecond supply device for supplying the fuel gas to the reformingcatalyst section; a sensor for detecting a temperature of the membranehydrogen separator; and a controller.

The controller functions to determine whether or not the temperature ofthe membrane hydrogen separator is greater than or equal to a targettemperature before the reforming catalyst section starts reformatereactions on the fuel gas; command the first supply device to supply thecombustion gas to at least one of the reforming catalyst section andhydrogen passage when the temperature of the membrane hydrogen separatoris smaller than the target temperature; and command the first supplydevice to stop the supply of the combustion gas and command the secondsupply device to start supply of the fuel gas to the membrane reactorwhen the temperature of the reforming catalyst section of the membranehydrogen separator reaches the target temperature.

The details as well as other features and advantages of this inventionare set forth in the remainder of the specification and are shown in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fuel reforming system according to a first embodiment ofthis invention.

FIG. 2 shows a map of the relationship between the pressure applied tothe membrane hydrogen separator and the target temperature for themembrane hydrogen separator.

FIG. 3 shows a flowchart describing a control routine according to afirst embodiment.

FIG. 4 shows a fuel reforming system according to a second embodiment.

FIG. 5 is a flowchart describing a control routine according to a secondembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic diagram of a fuel reforming system according to afirst embodiment.

A fuel reforming system according to this embodiment comprises avaporizer 1 for generating a fuel gas, a membrane reactor 2 forproducing pure hydrogen, that is to say, a membrane-type hydrogengenerator, a fuel cell 7 for generating power by electrochemicalreactions, and a combustor 14 for producing heat to warm-up the system.

The membrane reactor 2 comprises a combustion catalyst section 3 forsupplying heat required for the reforming reactions, a reformingcatalyst section 4 which performs reforming reactions, and a hydrogenpassage 6 allowing hydrogen separated by permeation through the membranehydrogen separator 5 from the reforming catalyst section 4 to bedischarged out of the membrane reactor 2.

The combustion catalyst section 3 comprises a catalyst such as platinum(Pt), palladium (Pd), or rhodium (Rh) which burns hydrogen in the anodeeffluent discharged from the fuel cell 7. The reforming catalyst section4 comprises a catalyst such as nickel (Ni), copper-zinc (Cu—Zn), orruthenium (Ru). The membrane hydrogen separator 5 separates thereforming catalyst section 4 and the hydrogen supply passage 6 in amembrane reactor 2. The membrane hydrogen separator 5 is made of ametal, such as palladium (Pd), a palladium alloy, vanadium (V), tantalum(Ta), or niobium (Nb). These metals have the property of storinghydrogen therein, resulting in permeability to hydrogen, and are subjectto hydrogen embrittlement at low temperatures rather than at hightemperatures. A temperature sensor 16 and a pressure sensor 17 areprovided on the membrane hydrogen separator 5.

The vaporizer 1 is a heat exchanger and is supplied with water and aliquid hydrocarbon fuel as the raw materials in order to produce a fuelgas. In the vaporizer 1, heat from the combustion gas supplied from thecombustion catalyst section 3 or the hydrogen passage 6 produces a fuelgas comprising a gaseous mixture of steam and hydrocarbon fuel fromwater and liquid hydrocarbon fuel by heat exchange. Fuel gas is suppliedto the reforming catalyst section 4 of the membrane reactor 2 via a fuelgas passage 33. Reformate reactions are performed on the fuel gas byheat exchange between the combustion catalyst section 3 and thereforming catalyst section 4. The membrane hydrogen separator 5 allowsselective permeation of hydrogen in the resulting reformate gas.Hydrogen is supplied to a fuel cell 7 through the hydrogen passage 6.The fuel cell 7 generates power by electrochemical reactions. Excesshydrogen, namely anode effluent, is discharged from the fuel cell 7 andsupplied to the combustion catalyst section 3 in the membrane reactor 2to burn excess hydrogen with air. The air is supplied from an aircompressor (not shown) and the air amount is controlled by a valve 31operated by a controller 15.

The reforming catalyst section 4 of the membrane reactor 2 performsreformate reactions on the hydrocarbon fuel. The hydrocarbon fuel maycomprise methanol, gasoline or natural gas. Reformate reactions will bedescribed below taking methanol reformate reactions as an example. Whenmethanol undergoes steam reforming reactions, methanol decompositionreactions as shown in Equation (1) and CO transformation reactions asshown in Equation (2) are simultaneously promoted. The overall reactionis shown in Equation (3). The reaction as shown in Equation (2) istermed a shift reaction.CH₃OH→CO+2H₂−90.0 (kJ/mol)  (1)CO+H₂O→CO₂+H₂+40.5 (kJ/mol)  (2)CH₃OH+H₂O→CO₂+3H₂−49.5 (kJ/Mol)  (3)

The fuel cell 7 comprises a pair of electrodes sandwiching anelectrolytic layer. One electrode, which is termed an anode, is suppliedwith a gas containing hydrogen. The other electrode, which is termed acathode, is supplied with a gas containing oxygen. An electromotiveforce is produced by electrochemical reactions occurring at bothelectrodes.

The electrochemical reactions occurring in the fuel cell 7 are shownbelow.H₂→2H⁺+2e−  (4)(½) O₂+2H⁺+2e−→H₂O  (5)H₂+(½) O₂→H₂O  (6)

Equation (4) represents reactions occurring at the anode and Equation(5) represents reactions occurring at the cathode. The overall reactionoccurring in the fuel cell 7 is shown in Equation (6).

A fuel cell 7 according to this embodiment is a proton exchange membranefuel cell (PEMFC) with electrodes provided with a catalyst comprisingplatinum. If a large concentration of carbon monoxide (CO) is containedin the reformate gas supplied to the fuel cell, the function of thecatalyst in the anode is adversely affected as a result of adsorption ofCO by the platinum catalyst. Consequently the membrane hydrogenseparator 5 reduces the CO concentration in the reformate gas suppliedto the fuel cell 7 to a level of several tens ppm.

Generally at startup of the fuel reforming system, the temperature ofthe membrane hydrogen separator 5 is low. If hydrogen is produced byreformate reactions in the reforming catalyst section 4 under theseconditions, embrittlement in the membrane hydrogen separator 5 mayresult from supplying hydrogen to the membrane hydrogen separator 5 at alow temperature. The hydrogen embrittlement reduces the permeationperformance of the membrane hydrogen separator 5.

The fuel reforming system according to this invention rapidly increasesthe temperature of the membrane hydrogen separator 5 to a targettemperature when starting the fuel reforming system in order to preventhydrogen embrittlement of the membrane hydrogen separator 5. Acontroller 15 sets the target temperature on the basis of the pressureapplied to the membrane hydrogen separator 5, i.e. the pressure on thereforming catalyst section 4. Below the target temperature, the membranehydrogen separator 5 is subject to hydrogen embrittlement when hydrogenis produced by reformate reactions in the reforming catalyst section 4.The fuel reforming system supplies combustion gas produced by thecombustor 14 respectively to the combustion catalyst section 3,reforming catalyst section 4 and the hydrogen passage 6 of the membranereactor 2. This fuel reforming system is provided with a main passagesupplying combustion gas to the membrane reactor 2 from the combustor14. The main passage branches into triple passages along the mainpassage. The triple passages comprise a first combustion gas passage 10to the reforming catalyst section 4 provided with a first flow controlvalve 11, a second combustion gas passage 12 to the hydrogen passage 6provided with a second flow control valve 13, and a third combustion gaspassage 8 to the combustion catalyst section 3 provided with a thirdflow control valve 9.

The fuel reforming system is provided with a combustion gas dischargepassage 18 for supplying exhaust gas from the combustion catalystsection 3 to the vaporizer 1 in order to supply heat required forvaporizing water and fuel. The fuel reforming system is further providedwith a reformate gas passage 22 which supplies exhaust gas from thereforming catalyst section 4 to the combustion catalyst section 3. Thefuel reforming system is further provided with a combustion gasdischarge passage 20 which branches via a switching valve 21 along thehydrogen supply passage 19 for supplying hydrogen to the fuel cell fromthe hydrogen passage 6. The combustion gas discharge passage 20 is adischarge passage for the combustion gas used to increase thetemperature of the membrane hydrogen separator 5 at startup.

Signals from a temperature sensor 16, signals from a pressure sensor 17and system startup command signals from the outside of the system areinputted into the controller 15. The controller 15 controls theclosing/opening of the flow control valves 9, 11, 13 based on thesesignals.

The controller 15 comprises a microcomputer provided with a centralprocessing unit (CPU), a read only memory (ROM), a random access memory(RAM) and an input/output interface (I/O interface). The controller 15may comprise a plurality of microcomputers.

After the start of the fuel reforming system and before the supply offuel gas to the reforming catalyst section 4, the controller 15 opensthe flow control valves 9, 11, 13 so that the combustion gas produced bythe combustor 14 is supplied to the hydrogen passage 6, the reformingcatalyst section 4 and the combustion catalyst section 3 of the membranereactor 2 through a combustion gas passage 8 to the combustion catalystsection 3, a combustion gas passage 10 to the reforming catalyst section4 and a combustion gas passage 12 to the hydrogen passage 6.

Further, the controller 15 controls the pressure on the reformingcatalyst section 4 by using a pressure control valve 34 disposed on thereformate gas passage 22 such that the pressure on the reformingcatalyst section 4 is maintained to a fixed value throughout startupoperation and normal operation of the reforming system. Therefore, onthe membrane hydrogen separator 5, the pressure of the combustion gas issubstantially equal to the pressure of the reformate gas.

Combustion gas supplied in this embodiment comprises a lean combustiongas not containing fuel in order to substantially avoid production ofhydrogen by the reforming catalyst section 4. The supply of a leancombustion gas does not cause hydrogen embrittlement in the membranehydrogen separator 5 although the supply of a fuel gas may causehydrogen embrittlement.

The temperature of the membrane hydrogen separator 5 is rapidlyincreased to a target temperature by supplying combustion gas in theabove manner and thus it is possible to avoid hydrogen embrittlement inthe membrane hydrogen separator 5 when the fuel gas is supplied to thereforming catalyst section 4.

The controller 15 further controls an injection valve 27 for thevaporizer 1 which introduces fuel from a fuel tank 25 into the vaporizer1, an injection valve 28 for the vaporizer 1 which introduces water froma water tank 26 into the vaporizer 1 and an injection valve 29 for thecombustor 15 which introduces fuel into the combustor 14. The controller15 also controls a valve 30 which supplies air from an air compressor(not shown) to the fuel cell 7.

The controller 15 monitors the pressure applied to the membrane hydrogenseparator 5 and the temperature of the membrane hydrogen separator 5using the temperature sensor 16 and the pressure sensor 17. In otherwords, the controller 15 monitors the pressure on the reforming catalystsection 4. When the temperature of the membrane hydrogen separator 5reaches a target temperature which depends on the pressure, thecontroller 15 controls the opening of the flow control valves 9, 11 13to take a value of zero in order to stop supply of combustion gas to themembrane reactor 2. Immediately after the target temperature is reached,the vaporizer 1 produces fuel gas by a supply of water and fuel gas andsupplies the fuel gas to the reforming catalyst section 4 in order tocommence reformate reactions.

In order to avoid hydrogen embrittlement of the membrane hydrogenseparator 5, reformate reactions are not performed until the temperatureof the membrane hydrogen separator 5 reaches a target temperature.Hydrogen embrittlement in the membrane hydrogen separator 5 tends tooccur when hydrogen is supplied at a low temperature and under highpressure. FIG. 2 is a map showing the relationship of the pressureapplied to the membrane hydrogen separator and the target temperature ofthe membrane hydrogen separator 5. This map is stored in the ROM of thecontroller 15.

Referring to FIG. 2, the region in which hydrogen embrittlement isproduced resides on the low-temperature side of the targettemperature—pressure curve in the figure. Since the membrane hydrogenseparator can not be used in this region, it is termed the “non-useregion”. This map is merely exemplary and corresponds to the use of apalladium membrane hydrogen separator. The target temperature normallyincreases as the pressure increases for a metal membrane hydrogenseparator. Referring again to FIG. 2, when hydrogen is supplied to amembrane hydrogen separator, high pressure results in hydrogenembrittlement even at high temperatures. In the case of a palladiummembrane hydrogen separator, hydrogen at partial pressure of 5atmospheres causes hydrogen embrittlement even at a high temperature of200° C.

Since the controller 15 controls the pressure control valve 34downstream of the reforming catalyst section 4 in order to control thepressure of the combustion gas or the pressure of the reformate gas to afixed value, the controller 15 sets a target temperature for themembrane hydrogen separator 5 in response to the pressure of thecombustion gas applied on the membrane hydrogen separator 5 duringstartup instead of the pressure of the reformate gas to be applied onthe membrane hydrogen separator 5.

Though hydrogen embrittlement is directly affected by the partialpressure of hydrogen in the reformate gas rather than the pressure ofthe reformate gas, the pressure of the combustion gas, which issubstantially equal to the pressure of the reformate gas in thisembodiment, is used for setting the target temperature. Since thepressure of the reformate gas is greater than the partial pressure ofhydrogen in the reformate gas, the target temperature is set to asufficiently high temperature for preventing hydrogen embrittlement ofthe membrane hydrogen separator 5 as a result of hydrogen in thereformate gas.

The production of hydrogen by reformate reactions occurs at relativelylow temperatures of about 100° C. As a result, reformate reactions areusually started once the temperature measured by the temperature sensor16 disposed on the membrane hydrogen separator reaches a targettemperature. Further, the target temperature for the membrane hydrogenseparator 5 at which reformate reactions commence increases as thepressure measured by the pressure sensor 17 disposed on the membranehydrogen separator 5 increases. In this manner, hydrogen embrittlementcan be avoided when reformate reactions commence.

Though the temperature of the membrane hydrogen separator 5 can beeffectively increased by supplying combustion gas to the reformingcatalyst section 4 and the hydrogen passage 6, the overall temperatureof the membrane reactor 2 is increased by the supply of combustion gasto the combustion catalyst section 3 in addition to the reformingcatalyst section 4 and the hydrogen passage 6. Consequently thedurability of the membrane reactor 2 is improved by suppressing thermalstrain resulting from the temperature distribution in the membranereactor 2.

Furthermore when combustion gas produced in the combustor 14 is suppliedto the reforming catalyst section 4, the hydrogen passage 6 and thecombustion catalyst section 3 of the membrane reactor 2, the controller15 controls the flow rate of combustion gas supplied to each section toan equal flow rate, with the first flow control valve 11 for thereforming catalyst section 4, the second flow control valve 13 for thehydrogen passage 6, and the third flow control valve 9 for thecombustion catalyst section 3. Pressure loss in the combustion catalystsection 3 and the reforming catalyst section 4 tends to be greater thanpressure loss in the hydrogen passage 6, because catalysts are supportedin the combustion catalyst section 3 and the reforming catalyst section4 and a retained body such as a fin is inserted into the catalystsections 3, 4. Therefore the controller 15 sets the opening of the flowcontrol valves 9, 11 to be greater than the opening of the flow controlvalve 13 to equalize the flow rate to each section and to optimize theeffectiveness of the temperature increase.

The flow rate to each section may be equalized by regulating thecross-sectional area (which is perpendicular to the flow direction) ofthe combustion gas passages 8, 10, 12. In other words, thecross-sectional area of the first combustion gas passage 10 and thethird combustion gas passage 8 may be set to be greater than thecross-sectional area of the second combustion gas passage 12.

Referring now to the flowchart shown in FIG. 3, an example of a controlroutine for starting the fuel reforming system will be described. Thisroutine is performed by the controller 15.

Firstly in a step S301, the pressure applied to the membrane hydrogenseparator 5 and temperature of the membrane hydrogen separator 5 areread by the controller 15 using a pressure sensor 17 and a temperaturesensor 16. Then the routine proceeds to a step S302 wherein a targettemperature is set based on the detected pressure by looking up thetemperature—pressure map shown in FIG. 2. Thereafter the routineproceeds to a step S303 wherein it is determined whether or not thedetected temperature is lower than the target temperature set in thestep S302. The processes performed in the step S302 and the step S303determine whether or not the detected temperature and pressure are inthe non-use region in which hydrogen embrittlement may be produced.

When the detected temperature is lower than the target temperature in astep S303, the routine proceeds to a step S304 wherein the switchingvalve 21 is commanded to switch the flow direction of gas from thedirection toward the fuel cell 7 to the direction toward the combustiongas discharge passage 20. Thereby deterioration of a platinum catalystin the fuel cell 7 is prevented by stopping supply of the combustion gasincluding tiny amounts of CO to the fuel cell 7.

Next the routine proceeds to a step S305 wherein air and fuel aresupplied to the combustor 14. In order to ensure complete combustion ofthe fuel, the air-fuel ratio is set to a lean value and lean combustionis performed in the combustor 14. Thereafter the routine proceeds to astep S306 wherein the flow control valves 9, 11, 13 are opened and thelean combustion gas not containing fuel is supplied to the membranereactor 2.

In the above manner, the supply of combustion gas to the membranereactor 2 increases the temperature of the membrane hydrogen separator5. Thereafter the routine returns to the step S301 and the process inthe steps S301–S303 is executed. When the temperature of the membranehydrogen separator 5 is not lower than the target temperature in thestep S303, that is to say, when the membrane hydrogen separator 5 can beused, the routine proceeds to a step S307. In the step S307, the firstflow control valve 11, the second flow control valve 13 and the thirdflow control valve 9 are closed. Further, the supply of fuel and air tothe combustor 14 is stopped and thus the generation of combustion gas isstopped. Thereafter in a step S308, fuel and water are supplied to thevaporizer 1, and thus fuel gas including steam and vaporized fuel issupplied to the reforming catalyst section 4 of the membrane reactor 2in order to commence reforming reactions in the reforming catalystsection 4. Further, the valve 31 is opened to supply air to thecombustion catalyst section 3 of the membrane reactor 2. Thereafter in astep S309, hydrogen which is produced and separated by the membranereactor 2 is supplied to the fuel cell 7 by switching the switchingvalve 21 to the fuel cell 7. At the same time, air is supplied to thefuel cell 7 and thus the fuel cell 7 generates power as a result of thesupply of air and hydrogen.

In this manner, during startup of the fuel reforming system, warming themembrane reactor 2 by using combustion gas not containing fuel preventsthe hydrogen embrittlement of the membrane reactor 2.

Hereafter referring to FIG. 4, a second embodiment of this inventionwill be described.

In FIG. 4, those components which are the same as those in FIG. 1 aredesignated by the same numerals and additional description will beomitted. The point of difference with respect to the first embodiment isthat in the second embodiment the combustion gas passage to the membranereactor 2 from the combustor 14 does not branch and constitutes only thecombustion gas passage 8 to the combustion catalyst section 3. Thecombustion gas passage extending from the combustion catalyst section 3branches to the first combustion gas passage 10 to the reformingcatalyst section 4 and the second combustion gas passage 12 to thehydrogen passage 6.

The effect of the second embodiment will be described hereafter. In thisembodiment, during startup of the fuel reforming system, combustion gasproduced by the combustor 14 is supplied only to the combustion catalystsection 3 of the membrane reactor 2 by passing through the thirdcombustion gas passage 8. The combustion gas supplied in this manner isa rich combustion gas containing fuel which is burnt in the combustioncatalyst section 3. A rich combustion gas containing residualuncombusted fuel is produced by enriching the air-fuel ratio withrespect to air and fuel supplied to the combustor 14. Lean combustion isperformed in the combustion catalyst section 3 by supplying a sufficientamount of air for burning the uncombusted fuel in the rich combustiongas to the combustion catalyst section 3, at the same time as adding therich combustion gas. Then, lean combustion gas produced by thecombustion catalyst section 3 is supplied to the hydrogen passage 6 andthe reforming catalyst section 4 of the membrane reactor 2 through thefirst combustion gas passage 10 connected to the reforming catalystsection 4 and a second combustion gas passage 12 connecting the hydrogenpassage 6.

Since the lean combustion gas supplied at this time does not containfuel, hydrogen resulting from reformate reactions is not produced in thereforming catalyst section 4. In this manner, the temperature of themembrane hydrogen separator 5 increases rapidly as a result of supplyingcombustion gas to each component of the membrane reactor 2 and thisresults in improved startability for the system. The controller 15monitors the pressure applied to the membrane hydrogen separator 5 andtemperature of the membrane hydrogen separator 5, and further performscontrol for starting reformate reactions once the temperature of themembrane hydrogen separator 5 reaches a target temperature. The targettemperature is set in consideration of the pressure applied to themembrane hydrogen separator 5. As the pressure becomes higher, thetarget temperature for the membrane hydrogen separator 5 at whichreformate reactions are commenced is increased. In this manner, it ispossible to ensure that hydrogen embrittlement is avoided.

Referring to the flowchart in FIG. 5, an exemplary control routineexecuted by the controller 15 for starting the fuel reforming systemwill be described.

In the same manner as the first embodiment, in a step S510, the pressureapplied to the membrane hydrogen separator 5 and the temperature of themembrane hydrogen separator 5 is read by the controller 15 by using thetemperature sensor 16 and the pressure sensor 17. The routine proceedsto a step S502 and a temperature—pressure map as shown in FIG. 2 islooked up in order to set a target temperature based on the detectedpressure. In a step S503, it is determined whether or not the detectedtemperature is lower than the target temperature. When the determinationresult in the step S503 is affirmative, the routine proceeds to a stepS504 wherein the switching valve 21 switches to a combustion gas exhaustpassage 20. Thereafter in a step S505, the supply of air and fuel to thecombustor 14 is commenced and a rich combustion gas is produced.

In a step S506, the third flow control valve 9 to the combustioncatalyst section 3 is opened thereby enabling supply of a richcombustion gas to the combustion catalyst section 3. In a step S507, airis supplied to the combustion catalyst section 3 and then ahigh-temperature lean combustion gas is produced by the combustioncatalyst section 3. Next, in a step S508, the first flow control valve11 to the reforming catalyst section 4 and the second flow control valve13 to the hydrogen passage 6 are opened, and thus a lean combustion gasis supplied to the reforming catalyst section 4 and the hydrogen passage6. The supply of combustion gas to the membrane reactor 2 increases thetemperature of the membrane hydrogen separator 5. Thereafter the routinereturns to a step S501 and the process in the steps S501–S503 isexecuted. When the detected temperature is not lower than the targettemperature in the step S503, the routine proceeds to a step S509wherein all the flow control valves 9, 11, 13 are closed. Then, in astep S510, the supply of air and fuel to the combustor 14 is stopped,and thus the supply of combustion gas to the membrane reactor 2 isstopped. Thereafter in a step S511, fuel and water are supplied to thevaporizer 1 and thus vaporized fuel gas is supplied to the reformingcatalyst section 4 of the membrane reactor 2. Further, supply of air tothe combustion catalyst section 3 of the membrane reactor 2 and the fuelcell 7 is commenced in the step S511. In a step S512, the switchingvalve 21 is switched to the fuel cell 7. In this manner, hydrogen istransferred to the fuel cell 7. The fuel cell 7 commences powergeneration by being supplied with hydrogen and air.

As shown in the above control routine, rich combustion gas produced bythe combustor 14 is supplied to the combustion catalyst section 3 andlean combustion is performed in the combustion catalyst section 3. Theresulting high-temperature combustion gas not including fuel is suppliedto the reforming catalyst section 4 and the hydrogen passage 6. In thismanner, the temperature of the hydrogen catalyst separator 5 iseffectively increased and the time required to startup the fuelreforming system is shortened.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above.

In the above two embodiments, a map is provided as shown in FIG. 2 todefine the relationship between the target temperature at whichreformate reactions are commenced and the pressure on the reformingcatalyst section 4. The controller 15 sets the target temperature basedon the pressure on the reforming catalyst section. Howeveralternatively, a map may be set showing the relationship of the targettemperature and the hydrogen differential pressure between the hydrogenpassage 6 and the reforming catalyst section 4. In this case, the fuelreforming system may be provided with a sensor detecting gas componentsand the pressure in both the reforming catalyst section 4 and thehydrogen passage 6. Subsequently, the differential pressure for hydrogenmay be calculated from the detection result of the sensor and the targettemperature may be set based on the hydrogen differential pressure.

The control method for starting the fuel reforming system according tothis invention is adapted to other fuel reforming systems using membranehydrogen separators 5. For example, control according to this inventioncan be applied to system in which the reforming catalyst section 4 isprovided independently from the membrane hydrogen separator 5.

In the above embodiments, combustion gas is supplied directly to thereforming catalyst section 4 in order to heat the membrane hydrogenseparator 5. However the membrane hydrogen separator 5 may be heated byheat exchange.

Furthermore, in the above embodiments, during startup, the reformingsystem maintains the pressure on the reforming catalyst section 4 to afixed value, and thus the pressure of the combustion gas is equal to thereformate gas. However, if the reforming system does not maintain thepressure on the reforming catalyst section 4 to a fixed value duringstartup, the controller 15 can also set the target temperature of themembrane hydrogen separator 5 not in response to the pressure ofcombustion gas but in response to the predicted partial pressure ofhydrogen in the reformate gas or the predicted pressure of the reformategas.

The entire contents of Japanese Patent Application P2001-284350 (filedSep. 19, 2001) are incorporated herein by reference.

Modifications and variations of the embodiments described above willoccur to those skilled in the art, in light of the above teachings. Thescope of the invention is defined with reference to the followingclaims.

1. A fuel reforming system comprising: a membrane reactor (2) having areforming catalyst section (4) for reforming a supplied fuel gas to areformate gas; a membrane hydrogen separator (5) for separating hydrogenfrom the reformate gas; a hydrogen passage (6) for transferring hydrogenseparated by the membrane hydrogen separator to a fuel cell (7); and acombustion catalyst section (3) for heating the reforming catalystsection; a first supply device (8,9,10,11,12,13,14,25,29) for supplyingcombustion gas to the membrane reactor, the first supply device having acombustor (14) for producing the combustion gas; a second supply device(1,25,26,27,28,33) for supplying the fuel gas to the reforming catalystsection; a sensor (16) for detecting a temperature of the membranehydrogen separator; and a controller (15) functioning to: determinewhether or not the temperature of the membrane hydrogen separator (5) isgreater than or equal to a target temperature before the reformingcatalyst section starts reformate reactions on the fuel gas; command thefirst supply device to supply the combustion gas to at least one of thereforming catalyst section and hydrogen passage when the temperature ofthe membrane hydrogen separator is smaller than the target temperature;and command the first supply device to stop the supply of the combustiongas and command the second supply device to start supply of the fuel gasto the reforming catalyst section of the membrane reactor when thetemperature of the membrane hydrogen separator reaches the targettemperature.
 2. The fuel reforming system as defined in claim 1, whereinthe first supply device comprises a first passage (10) for transferringthe combustion gas from the combustor to the reforming catalyst sectionand a first valve (11) provided in the first passage in order toregulate a flow rate of the combustion gas in response to a command fromthe controller (15); and wherein the controller (15) further functionsto command the first valve (11) to allow flow of the combustion gas whenthe temperature of the membrane hydrogen separator is smaller than thetarget temperature.
 3. The fuel reforming system as defined in claim 1,wherein the first supply device comprises a second passage (12) fortransferring the combustion gas from the combustor to the hydrogenpassage and a second valve (13) provided in the second passage in orderto regulate a flow rate of the combustion gas in response to a commandfrom the controller (15); and wherein the controller (15) furtherfunctions to command the second valve to allow flow of the combustiongas when the temperature of the membrane hydrogen separator is smallerthan the target temperature.
 4. The fuel reforming system as defined inclaim 1, wherein the first supply device comprises a third passage (8)for transferring the combustion gas from the combustor to the combustioncatalyst section and a third valve (9) provided in the third passage inorder to regulate a flow rate of the combustion gas in response to acommand from the controller (15); and wherein the controller (15)further functions to command the third valve to allow flow of thecombustion gas when the temperature of the membrane hydrogen separatoris smaller than the target temperature.
 5. The fuel reforming system asdefined in claim 1, wherein the combustor (14) in the first supplydevice produces a lean combustion gas not containing fuel.
 6. The fuelreforming system as defined in claim 1, wherein the combustion gasproduced by the combustor (14) contains fuel; and wherein the firstsupply device comprises a first passage (10) for transferring thecombustion gas from the combustion catalyst section (3) to the reformingcatalyst section (4), the first passage being provided with a firstvalve for regulating a flow rate of the combustion gas in response to acommand from the controller (15), and a third passage (8) transferringthe combustion gas from the combustor (14) to the combustion catalystsection (3), the third passage being provided with a third valveprovided for regulating a flow rate of the combustion gas in response toa command from the controller (15); wherein the combustion catalystsection (3) burns the fuel contained in the combustion gas; and whereinthe controller (15) further functions to command the first and thirdvalves (9,11) to allow flow of the combustion gas when the temperatureof the membrane hydrogen separator (5) is smaller than the targettemperature.
 7. The fuel reforming system as defined in claim 1, whereinthe combustion gas produced by the combustor contains fuel; and whereinthe first supply device comprises a second passage (12) transferring thecombustion gas from the combustion catalyst section (3) to the hydrogenpassage (6), the second passage being provided with a second valve (13)for regulating a flow rate of the combustion gas in response to acommand from the controller (15), and a third passage (8) transferringthe combustion gas from the combustor (14) to the combustion catalystsection (3), the third passage being provided with a third valve (9)provided in the third passage for regulating the flow rate of thecombustion gas in response to a command from the controller (15);wherein the combustion catalyst section (3) burns the fuel in thecombustion gas; and wherein the controller (15) further functions tocommand the second and third valves to allow flow of combustion gas whenthe temperature of the membrane hydrogen separator (5) is smaller thanthe target temperature.
 8. The fuel reforming system as defined in claim1, wherein the first supply device supplies the combustion gas to thehydrogen passage (6), the reforming catalyst section (4) and thecombustion catalyst section (3) so that the flow rate to the hydrogenpassage, the reforming catalyst section and the combustion catalystsection is substantially equal.
 9. The fuel reforming system as definedin claim 8, wherein the first supply device comprises a first valve (11)for regulating a flow rate of the combustion gas to the reformingcatalyst section (4) in response to a command from the controller (15),a second valve (13) for regulating a flow rate of the combustion gas tothe hydrogen passage (6) in response to a command from the controller(15), and a third valve (9) for regulating a flow rate of the combustiongas to the combustion catalyst section (3) in response to a command fromthe controller; and wherein the controller (15) controls the first,second and third valves so that the flow rate to the hydrogen passage,the reforming catalyst section and the combustion catalyst section issubstantially equal.
 10. The fuel reforming system as defined in claim 8wherein the cross-sectional area of a passage (12) transferring thecombustion gas to the hydrogen passage (6) is smaller than thecross-sectional area of a passage (10) transferring the combustion gasto the reforming catalyst section (4) and the cross-sectional area of apassage (8) transferring the combustion gas to the combustion catalystsection (3).
 11. The fuel reforming system as defined in claim 1,further comprising a sensor (17) for detecting a pressure applied to themembrane hydrogen separator (5); wherein the controller (15) furthersets the target temperature for the membrane hydrogen separator inresponse to the pressure applied to the membrane hydrogen separator sothat the target temperature increases as the pressure increases.
 12. Astartup controlling method for use in a fuel reforming system; the fuelreforming system comprising: a membrane reactor (2) having a reformingcatalyst section (4) for reforming a supplied fuel gas to a reformategas, a membrane hydrogen separator (5) for separating hydrogen from thereformate gas, a hydrogen passage (6) for transferring hydrogenseparated by the membrane hydrogen separator to a fuel cell (7), and acombustion catalyst section (3) for heating the reforming catalystsection; a first supply device (8,9,10,11,12,13,14,25,29) for supplyingcombustion gas to the membrane reactor, the first supply device having acombustor (14) for producing the combustion gas; a second supply device(1,25,26,27,28,33) for supplying the fuel gas to the reforming catalystsection; a sensor (16) for detecting a temperature of the membranehydrogen separator; the method comprising: determining whether or notthe temperature of the membrane hydrogen separator (5) is greater thanor equal to a target temperature before the reforming catalyst sectionstarts reformate reactions on the fuel gas; commanding the first supplydevice to supply the combustion gas to at least one of the reformingcatalyst section and hydrogen passage when the temperature of themembrane hydrogen separator is smaller than the target temperature; andcommanding the first supply device to stop the supply of the combustiongas and commanding the second supply device to start supply of the fuelgas to the reforming catalyst section of the membrane reactor when thetemperature of the membrane hydrogen separator reaches the targettemperature.
 13. A fuel reforming system comprising: a membrane reactorhaving a reforming catalyst section for reforming a supplied fuel gas toa reformate gas; a membrane hydrogen separator for separating hydrogenfrom the reformate gas; a hydrogen passage for transferring hydrogenseparated by the membrane hydrogen separator to a fuel cell; and acombustion catalyst section for heating the reforming catalyst section;a first supply device for supplying combustion gas to the membranereactor, the first supply device having a combustor for producing thecombustion gas; a second supply device for supplying the fuel gas to thereforming catalyst section; a sensor for detecting a temperature of themembrane hydrogen separator; means for determining whether or not thetemperature of the membrane hydrogen separator is greater than or equalto a target temperature before the reforming catalyst section startsreformate reactions on the fuel gas; means for command the first supplydevice to supply the combustion gas to at least one of the reformingcatalyst section and hydrogen passage when the temperature of themembrane hydrogen separator is smaller than the target temperature; andmeans for commanding the first supply device to stop the supply of thecombustion gas and commanding the second supply device to start supplyof the fuel gas to the reforming catalyst section of the membranereactor when the temperature of the membrane hydrogen separator reachesthe target temperature.